So my first question is, do you want to become a Wiccan? Or are you merely interested in studying the beliefs and practices of Wicca as you have studied other religions? If it's the latter then perhaps you can comfort your Aunt by explaining that you are simply looking at it from a scholarly standpoint, not as one who is actually going to become a practitioner of that religion.
If you are actually looking at becoming Wiccan and turning away from your Christian beliefs, that is really a choice that only you can make. You can thank her for her concern as was already mentioned. Or you can simply not discuss the topic around her where it can distress her. (I'm assuming you're not living under her roof!)
But how best to approach her is going to depend very much on what sort of interest you truly have in Wicca.